The invention pertains to the field of nonlinear optical frequency mixing processes and systems.
Lasers are used in a wide array of applications ranging from military to medical uses. Depending on the application, different laser wavelengths may be required. This can be accomplished through the use of Non-Linear Optic (NLO) crystals, which convert the wavelength of light passing through them. However, the generation of radiation at maximum output requires alignment of the optical axis of birefringent crystals at the proper phasematching angle with respect to the direction of propagation of incident laser beams. The phasematching angle is a function of laser frequency and also temperature. This causes the intensity of the radiation which results from the nonlinear mixing process in the crystal to drop off sharply if the frequency of the incident beam varies, if the crystal is rotated slightly from the proper phasematching angle, or if the crystal heats up upon the passage of the laser beams therethrough or due to room temperature fluctuations. In order to return to maximal output, the realignment of the crystal with respect to the beam becomes necessary. The problem becomes amplified in laser systems utilizing many nonlinear optical frequency mixing processes or for systems that need to vary laser frequencies.
One approach to phasematching is described in U.S. Pat. No. 4,187,027 to Bjorklund et al, which is incorporated by reference in its entirety, uses a servo-motor to rotate the crystal mount to achieve phasematching. However, one of the drawbacks to this approach is the potential outgassing component generated by the servo-motor which can eventually cloud up the crystal or be too large to fit in current laser systems.
To optimize this process, NLO crystals should be tuned to maximize energy that is to be converted. This is typically done in two ways, temperature adjustment or regulation and angular rotation to achieve maximum efficiency for the crystal. Once tuned the laser system is then sent to the customer. This is both expensive and time-consuming where the laser system has to be sent back for retuning at a later date.